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So basically my fork code is running really wack. I am sure the problem is something simple, I just can't see it. For some reason my fork() is not completing all the way. Like the first printf is not printing, yet the 2nd printf, which is commented; if I uncomment it, it prints the first and 2nd printf, but nothing after that seems to print for the child. The execv process also does not seem to run, even though it was running at one point. 

#include <stdio.h>
#include<unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
int main(int argc, char *argv[]){
char input[200];
char path[]="/bin/";
char str[80];

do{
printf("dash> ");
fgets(input, 200, stdin);
input[strcspn( input, "\n" )] = '\0';
char* token = strtok(input, " ");
// printf("TEST: %s",token);
strcpy(str, path);
strcat(str, token);
// printf("str1: %s", str);
int rc=fork();
if(rc<0){  // fork failed
 printf("Error");
return 0;
}
   else if(rc==0){//child process
    printf("hello toekn is: %s ",token);
   // printf("\nhello, I am child (pid:%d)\n", (int) getpid());
   // char* arr[] = {"ls", NULL};
   // printf("hello, I am child");
   char *myargs[15];
   myargs[0]=token;
   int counter=0;
   printf(token);
   while(myargs[counter] != NULL){
   counter++;
   myargs[counter]=strtok(input, " ");
   printf(myargs[counter]);
   }
   // myargs[1]=token;
    myargs[counter+1]=NULL;

   execv(str,myargs );
   printf("failed");
  }
   else{ //parent process
     int rc_wait=wait(NULL);
     printf("hello, I am parent of %d (rc_wait:%d) (pid:%d)\n", rc, rc_wait, 
  (int) getpid());

 // printf("\nHello %d", rc_wait);
}

 }while(strcmp(input,"exit")!=0);
 return 0;
}

So for example when the 2nd printf in the child is not commented this is the output: 

dash> ls
hello toekn is: ls
hello, I am child (pid:33522)
hello, I am parent of 33522 (rc_wait:33522) (pid:33095)
dash>

And when it is commented :

 dash> ls
 hello, I am parent of 4017 (rc_wait:4017) (pid:3377)
 dash>

As you can see for some reason, because the first printf is commented out the 2nd one also does not display. As well as the rest of the child process.

I feel like the problem is the child process does not complete in time, of the wait in parent. If anyone can help I would greatly appreciate it. Thanks

Using gcc (GCC) 4.8.5

Adil Hamid
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    Try adding `fflush(stdout)` immediately before the `execv`. If that fixes everything, I will explain. – zwol Sep 05 '18 at 21:43
  • @zwol the output was the same, nothing changed. – Adil Hamid Sep 05 '18 at 21:48
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    Look hard at whether [`printf()` anomaly after `fork()`](https://stackoverflow.com/questions/2530663/) can help you. It is hard to know what code does what when there are comments all over the place. I suggest embedding the version that reproduces the trouble in the question, or use conditional compilation (`#ifdef DEBUG_FORK` / `#else` / `#endif` around the print statements, and show the output when compiled with `-DDEBUG_FORK` and without it). It is much easier than us having to guess what we need to look at. Indenting the code for readability would help. See also MCVE ([MCVE]). – Jonathan Leffler Sep 05 '18 at 22:01
  • Distracting that `str[80];` is so much smaller than `input[200];` and susceptible to `strcat(str, token);` overrun. – chux - Reinstate Monica Sep 05 '18 at 22:38
  • I changed code to `assert(counter < 15); myargs[counter] = strtok(input, " ");`, ran and the assertion failed. – chux - Reinstate Monica Sep 05 '18 at 22:46
  • `while (myargs[counter] != NULL) { counter++; myargs[counter] = strtok(input, " "); printf(myargs[counter]); }` makes little sense to attempt `printf(NULL)`. The check for `myargs[counter] != NULL` needs to occur before `printf()`. – chux - Reinstate Monica Sep 05 '18 at 22:49
  • Suggest `input[strcspn( input, "\n\r" )] = '\0';` (Add `\r`) to eliminate a potential input issue. – chux - Reinstate Monica Sep 05 '18 at 22:59
  • @chux I changed the str and input sizes to match more.Anyway I figured out the problem, in my while loop, when using strtok, I replaced input with NULL and it started working. All the printf statements and execv. Still dont understand why the printf before that line were not working but whatever. – Adil Hamid Sep 06 '18 at 04:16
  • Always put a newline at the *end* of each output line. Read about stdout buffering. You'll find lots of questions here about the subject. – rici Sep 06 '18 at 04:52

0 Answers0